During typical surgical procedures, an opening in the tissue is created and then held open using a retractor, thereby allowing the surgeon to access the tissue(s) being treated. There are numerous designs and styles of retractors which are used for various surgical procedures. In all cases, preventing unnecessary injury to the patient is desirable. Trauma to the patient can be reduced by creating a smaller incision in the tissue. The employment of surgical techniques and accompanying instruments that reduce the size of the incision, and in-turn damage to the surrounding tissues, is generally referred to as “minimally invasive surgery” (MIS). One of the drawbacks to MIS procedures is that it forces the surgeon(s) to perform the complex and critical tasks of the surgery in a reduced work space.
Special surgical instruments have been developed to reduce the negative effects of working in a reduced space including, for example, retractor 100 shown in FIG. 1. There is a wide array of surgical retractors that use a frame 101 to which various retractor blades 102 or other tissue manipulating implements are affixed. The frame 101 is comprised of a basic rack and pinion mechanism that both separates and secures the retractor arms 103 and 104. The rack and pinion system, having a fixed hinge point on one end of the toothed rack, as well as the carriage 105 that travels along the rack and contains the pinion gear, rotated by a knob 106, and locked in position by a pawl mechanism 107, are commonly used by many providers of surgical retractors. This style of retractor is typically oriented with the rack perpendicular to the long axis of the patient's body so that tissue is separated in the medial-lateral direction. Therefore, it is commonly referred to as a “transverse” retractor. From the initial hinge points on the fixed end and carriage, moving towards the tip, changes in the design begin to appear depending on the application. Different arms are made to attach blades or hooks for separating tissue, attaching to screws to separate vertebrae, and many other applications. However, this standard frame design is employed on all of these retractor systems despite the varying working ends (e.g., blades 102).
The frame 101 supports the arms 103 and 104 which hold the retractor blades 102 in place. The blades 102, in turn, hold back the tissues once inserted into the incision 108. In transverse retractor systems, the tissue is spread apart using the rack and pinion mechanism on the frame 101 that allows for one degree-of-freedom (DOF) movement to facilitate the dilation. In many cases, the retractor blades 102 are allowed to rotate along their long axis 109 (perpendicular to the incision 108) to align with the contacting tissue. Furthermore, the arms 103 and 104 which connect the retractor blades 102 to the frame 101 can include a series of hinge points 110 allowing them to articulate in a manner that allows the device to conform closer to the skin. Typically, the long axis 109 of the blade(s) is constrained to motion residing in a single plane 111 relative to the frame 101 while facilitating the primary tissue separation.
Some mechanisms have been developed to provide an additional DOF to the blades of a retractor, facilitating a secondary angular direction of tissue retraction. FIG. 2 shows an example of this out of plane rotation for both blades of a retractor 200. This added DOF allows the arm(s) that secure the retractor blades to rotate outwards in a manner such that the proximal (to the patient) tip(s) of the retractor blades separate further from each other. This added rotation of the retractor arm creates a “toe in” effect at the blade (into the tissue), which displaces tissue without the need to enlarge the incision. This is desirable because the size of the incision (at the surface of the skin) is not noticeably increased; thereby reducing trauma while increasing the working space at the surgical target site.
Existing mechanisms for providing the “toe in” effect for the working ends of a retractor have numerous undesirable qualities. For example, U.S. Pat. No. 7,537,565 discloses a retractor 200 (FIG. 2) that includes a mechanism whereby a raised knob is turned to drive a screw that separates two otherwise flush metal surfaces. The separation forms an angle and gap between the surfaces which corresponds with the “toe in” angle of rotation for the blade. This mechanism is bulky for retractors, where minimal size and a low, conforming profile relative to the incision on the surface of the patient's exterior are highly desired if not required. Furthermore, the mechanism is entirely exposed to the surgical environment, introducing problems with sanitizing and maintaining the instrument between uses.